Wood Microbiology

Decay and Its Prevention

Robert A. Zabel, Jeffrey J. Morrell

• Publisher: Academic Press
• Year: 2020
• ISBN:
  9780128205730
• Edition: 2
• Topic: Biowissenschaften
• Subtopic: Botanik

Wood Microbiology, Second Edition, presents the latest advances in wood decay and its prevention. Coverage includes classification of fungi and bacteria, factors affecting growth and survival, fungal metabolism, and wood chemistry. There are also chapters that focus on the anatomical aspects, chemical changes, and ultrastructural effects of wood decay. Additionally, this book discusses major issues associated with wood decay, detecting decay, and how to take protective action against it.

This is a one-stop reference resource for wood scientists, wood processing and preserving professionals, foresters and forest pathologists, as well as students of forestry, and wood science and technology courses. It is authored by two leading experts with over 80 years of experience working with timber durability.

• Provides updated taxonomy and classification of decay groups
• Presents detailed descriptions of anatomical, chemical, and ultrastructural aspects of wood decay
• Includes discussions on major issues associated with decay, how to detect decay and preventative measures

Chapter One

Introduction to wood microbiology

Abstract

The major positive and negative attributes of wood are discussed. The field of biodeterioration is reviewed in relation to its origins from Forest Pathology. The roles of various researchers in understanding the nature of deterioration are reviewed to provide context then common terminology related to degradation is reviewed.

Keywords

Forest pathology; mycology; biodeterioration; durability; fungi; bacteria

Contents

Outline

• Wood - a remarkable material 2
• Wood value and uses 3
• Potential uses of wood 3
• Wood disadvantages 4
• Decay losses and future wood needs 5
• Reducing decay losses 5
• Wood pathology vs wood microbiology 6
• Historical perspectives of wood pathology 7
• Concepts and terminology in wood microbiology 13
• Summary 15
• References 16
• Sources of Historical Information on Early Developments in Forest Pathology, Wood Pathology, and Wood Preservation 17

This textbook focuses primarily on the damaging decays and discolorations that fungi may cause to wood under some use-conditions. A major emphasis is placed on recognition, causes, conditions favoring development, effects on various wood use properties, and prevention or control of these serious wood defects.

This introductory chapter begins with a review of the unique qualities of wood for a wide range of uses and the benefits of its production. This is done to put the negative effects that may occur in some wood uses into proper perspective. It is not too early to emphasize that most wood defect problems can be avoided or greatly minimized when wood us properly used or handled.

Other agents that may degrade or destroy wood are briefly discussed because their damage can be confused with decay. Wood decay losses at various stages of production and use are reviewed to justify the level of control effort and suggest research priorities. The historical aspects of major wood decay understandings are traced to establish its relation to other related fields, and probable emergence as a specialized facet of microbiology. The fungal cause of decay resulted in much of the early information on decay appearing in phytopathological or mycological journals. Unfortunately, this early information on decay prevention and controls failed to reach engineering and architectural sources where the design of wood structures was determined. Later, we will see that design of structures in terms of water shedding or retention can be crucial to effective decay prevention. The introductory chapter ends with some basic concepts, and the definitions of some terms that will be used throughout the book.

Wood - a remarkable material

Wood is a remarkable material of great value and importance in the world economy. It is used extensively as a structural material, fuel, or industrial raw material in many parts of the world. It is estimated that wood accounts for one-fourth of the value of the major industrial materials in the United States (National Research Council, 1990). As a renewable natural resource, it is available in large quantities at relatively low costs. An estimated one-third of the landed area of the world is in forests. As a land crop, wood supplies can be increased in both volume and quality by wise forest management practices. Wood production in the forest ecosystem is often associated with many other forest values and amenities such as soil development and enrichment, wildlife resources, moderating and extending water run-off, providing superb recreational settings, reducing atmospheric pollution, and landscape aesthetics. More recently, forests have also been examined for their possible roles as carbon sinks for sequestration of atmospheric carbon dioxide to slow the rate of global climate change

Wood is also unique in a plant evolutionary sense since it was the vertical development of perennial vascular tissue (wood) that led to the aerial development of land plants. The vertical stem or trunk of the tree consists of elongated cells with unusual strength, flexibility, and durability both at macroscopic and ultrastructural levels. These properties permit stems to bear heavy crown loads and to withstand high horizontal stress from wind and ice loads. The long-term selection for these properties has led to many unique properties of wood.

Wood value and uses

As a structural material, wood has high strength per unit weight, and is easily shaped and fastened. It is a convenient energy source and a major inexpensive source of cellulose and its many derivatives for the chemical industry. The color patterns and textures of woods are often pleasing, leading to uses for many decorative purposes. Wood is available in a wide range of textures, colors, densities, and chemical compositions supporting a wide range of important uses such as construction timbers and lumber, decorative paneling, plywood, piling and wharves, railroad ties, poles and posts, packaging and crates, paper and paper products, cellulose derivatives, charcoal, and thousands of specialized miscellaneous uses ranging from pipe bowls to fiddle heads. It is important to note that, despite its use in a variety of structural applications, over half of the wood consumed each year on the planet is burned for either cooking or energy production.

Potential uses of wood

Wood looms even more significantly as a valuable raw material in the future as expanding world populations place increasing stress on natural land ecosystems as sources for food, fiber, and energy. Modern intensive forestry practices have the potential to substantially increase both the yields and quality of wood. Trees are efficient radiant energy transducers in many regions and their biomass can be converted to alcohol, as alternative combustion engine energy sources. This process is already well underway for production of aviation fuels. The selective decay actions of fungi and related fermentation activities may permit the utilization of wood as cheap sources of animal feed or protein. As a material, wood is readily biodegradable under certain conditions and returns natural substances to ecosystem cycling. It has low energy requirements for conversion into various products as compared with other structural materials. As relative raw materials costs and availability change, wood has the potential to replace petroleum as a base for the production of a wide range of industrial chemicals and polymers and perhaps energy itself. Although not considered as often, the simple use of wood in a structure effectively sequesters this carbon for the life of the structure and potentially beyond further enhancing the potential influence of timber on atmospheric carbon dioxide levels. Use of wood in properly designed structures is an important aspect of this process.

Wood disadvantages

Wood has some serious disadvantages that limit its usefulness for some purposes, including:

1. 1. Wood is primarily biodegraded by the action of fungi and, under the proper conditions, these fungi may decay and weaken or discolor the wood to the point where replacement is required. Other biological agents also attack wood. Termites are a serious threat to untreated wood in many tropical regions. Marine invertebrates chew tunnels in wood in various salt water uses and cause serious damage. These other bioagents that can degrade or destroy wood are discussed in Chapter 2. In many cases, their actions can be controlled or minimized by judicious use of treated or naturally durable wood.
2. 2. Wood combusts at low kindling temperatures and, in certain size configurations and conditions, burns readily. Chemical treatments and wood design can reduce the combustion hazard. One advantage of wood is that it burns at a predictable rate and rarely fails catastrophically.
3. 3. Wood is dimensionally unstable at moisture contents below the fiber saturation point (fsp) and swells as it wets and shrinks as it dried. This problem is compounded because the largest dimensional changes occur in the tangential plane. Differential shrinkage often leads to deep check formation in the radial plane in round stock such as poles or piling. Chemical treatments may reduce the dimensional changes, but these treatments are expensive.
4. 4. Wood, as a natural product, displays considerable variability in its appearance, chemical composition, and physical properties. Some differences are the result of species or growth conditions and are accounted for in specifications. High safety factors in critical design uses of wood are used to minimize this disadvantage. Conversely, the variability in color and texture of wood provides its beauty and aesthetic appeal for many home uses.
5. 5. Wood has a large bulk per unit weight for fuel, pulping and chemical uses

In summary of this brief discussion of wood disadvantages, it is stressed that effective wood handling, properly designed and maintained structures, chemical treatments, and proper use of standards and specifications, can dramatically minimize these disadvantages. In a long-term environmental setting, the biodegradability of wood may also minimize accumulation of solid wastes created when less degradable materials such as plastics are used.

Decay losses and future wood needs

Accurate estimates of decay losses are useful to justify controls and serve as research incentives. Decay losses are difficult to quantify because of the multiplicity of wood uses under a wide range of environmental conditions. Experienced guesses are that 10% of the annual timber cut in the United States is used to replace wood that decayed in service, much of it primarily from improper use and care. Added to this base raw material cost would be, in many cases, the added costs representing processing, fabricating, finishing, merchandising, and assembly or replacement operations. The substantial labor costs incurred by replacement and, in some cases, the inconvenience of interrupted services would have to be added. Another subtle loss source may be eventual wood replacement by more expensive, less environmentally friendly, and less satisfactory materials.

Large additional supplies of wood are required to meet burgeoning population needs beyond the next century. A substantial first step in meeting future timber needs may be simply to handle and use wood more effectively, thereby drastically reducing decay losses. In a related sense, forest pathologists and entomologists recognize that control of tree diseases and forest insect pest problems also can dramatically increase future wood supplies.

Reducing decay losses

Properly used wood is an amazingly durable organic material. Only a few specialized microorganisms, primarily the higher fungi, have solved the biochemical riddle of its rapid digestion. Experts agree that much is already known about effective and economical control of decay in most wood uses. The central control problem is that much of this information is fragmented and not readily available or generally known by wood processors, designers, merchandisers, and users. Most architecture and engineering students learn relatively little about wood compared to steel and concrete, yet many go on to careers designing with wood. Until recently, wood has been available at low ...